1. Field of the Invention
The invention relates to insulating safety plugs for insertion into receptacles of locking female electrical connectors of arc welders.
2. Description of the Prior Art
Arc welding machines supply very high DC currents to welding "sticks" which are rididly gripped by means of hand-held clamping devices. The welding sticks and the clamping devices are electrically conductive. A clamping device is coupled to a female electrical connector by means of a male electrical connector inserted into the female electrical connector. The female electrical connector, which is manufactured by Tweco Products, Inc., is connected to an arc welder by means of a heavy, well insulated single conductor cable. The female connector includes a heavy brass core covered with heavy rubber insulation. The brass core has one end connected to the conductor of the cable within the rubber insulation, the other end of the brass core being exposed. The exposed end of the brass core is circular, and lies in a plane perpendicular to a cylindrical axis of the brass core. The exposed end of the brass core of the female connector is recessed only slightly from the edge of the heavy rubber insulator encasing the brass core. A cylindrical hole for receiving a cylindrical conductive prong of the male connector is disposed concentrically along the cylindrical axis into the exposed end of the base core. A ridge is disposed deep in the cylindrical hole, forming a chord member extending between two portions of the wall of the cylindrical hole.
The conductive prong of the male connector includes a cylindrical shaft having a circumferential groove disposed around the shaft adjacent a tip portion of the shaft of the prong. The tip portion of the shaft extending beyond the circumferential groove includes a "cutaway portion" having a flat surface parallel to an axis of the conductive prong and extending from the bottom of an adjacent portion of the circumferential groove to the outer end of the tip portion of the shaft. The flat surface passes by the chord member as the conductive prong is inserted into the cylindrical hole so that the chord member is essentially aligned with the circumferential groove when the shaft of the male connector is inserted as far as possible into the female connector. The male and female connectors are then twisted in opposite directions, causing the chord member to pass into the circumferential groove, thereby tightly engaging the shaft of the male connector. This results in a very low resistance electrical connection from the base core of the female connector to the shaft of the male connector, which is connected to the welding stick by means of the clamping device. The low resistance electrical connection is essential (because of very high currents generated by the arc welder) to avoid overheating of the male and female electrical connectors and also to avoid voltage drops across them.
In order to obtain the low resistance electrical contact between the male and female electrical connectors, and to attain precise, reliable locking action as described above, it is necessary that the above described cylindrical hole in the brass core of the female connector be precisely matched to the cylindrical shaft of the male connector.
In use, welders wear electrically insulated gloves when using an arc welder. The voltage produced by the arc welding machine is applied via the above described cable, female connector and male connector to the welding stick. The remote tip of the welding stick is touched to a metal object to be welded, the metal object being electrically grounded. A very high current then flows from the tip of the welding stick. The temperature of the tip of the welding stick rapidly rises to its melting point, as does the metal portion of the metal object touched by the tip of the welding stick. Welding is thus achieved by fusing of the melted metal of the welding stick and the object being touched by the welding stick.
When a welder has completed a welding task, he must, of course, disconnect the welding stick from the high voltage to which it is connected (by means of the male connector) before he sets the welding stick and clamp down to avoid shorting of the clamp and/or welding stick to any electrically grounded object that may be in the vicinity. He does this by twisting the male and female connectors, essentially as described above, to allow the cutaway portion of the shaft of the male connector to slip under the chord member, unlocking the two connectors. He then separates the two connectors.
At this point, many, if not most welders, simply drop the female connector to the floor, often carelessly. Since the base core still has a high voltage thereon, if the female connector is dropped on or adjacent to any electrically grounded conductive object, the exposed end of the brass core will be shorted to ground. A very large current will flow through the part of the brass core touching the grounded object. This causes melting of material of the brass core, the formation of a "bead" of brass thereon. The bead then hardens. If the bead is located at the edge of the cylindrical hole in the base core, the precision prong or shaft of the male connector can no longer be inserted into the cylindrical hole of the female connector until the bead is filed off or otherwise removed. As a practical matter, the female connector, which costs roughly $6.00 to $7.00, is discarded and replaced by a new one.
Accordingly, it is an object of the invention to provide a means and method for avoiding shorting of the brass core of female electrical connectors of arc welders when the female connectors are disconnected from male connectors